Catalytic hydrogenation using complexes of base metals with tridentate ligands

ABSTRACT

Complexes of cobalt and nickel with tridentate ligand PNHP R  are effective for hydrogenation of unsaturated compounds. Cobalt complex [(PNHP Cy )Co(CH 2 SiMe 3 )]BAr F   4  (PNHP Cy =bis[2-(dicyclohexylphosphino)ethyl]amine, BAr F   4 =B(3,5-(CF 3 ) 2 C 6 H 3 ) 4 )) was prepared and used with hydrogen for hydrogenation of alkenes, aldehydes, ketones, and imines under mild conditions (25-60° C., 1-4 atm H 2 ). Nickel complex [(PNHP Cy )Ni(H)]BPh 4  was used for hydrogenation of styrene and 1-octene under mild conditions. (PNP Cy )Ni(H) was used for hydrogenating alkenes.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of and claims priority to and thebenefit of U.S. patent application Ser. No. 13/587,717 filed Aug. 16,2012, the entire content of which is incorporated herein.

STATEMENT REGARDING FEDERAL RIGHTS

This invention was made with government support under Contract No.DE-AC52-06NA25396 awarded by the U.S. Department of Energy. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The invention relates to catalytic hydrogenation of unsaturatedcompounds using complexes of base metals with tridentate ligands.

BACKGROUND OF THE INVENTION

Catalytic hydrogenation is used for the production of bio-renewablechemicals, fuels, commodity chemicals, fine chemicals, andpharmaceuticals. Complexes of precious metals (e.g. Rh, Ir, Ru, Pd, orPt) and ligands are used for catalytic hydrogenation. They exhibit highfunctional group tolerance, have long lifetimes and high activities, andmay be used for hydrogenating carbonyl (C═O) groups, alkene (C═C)groups, alkyne (C≡C) groups, imine (C═N) groups, nitrile (C≡N) groups,and the like. Complexes of the precious metals rhodium, ruthenium, andiridium have been used for asymmetric catalytic hydrogenation. Thedevelopment of base-metal-containing complexes (e.g. complexes of Mn,Fe, Co, Ni, Cu, and the like) for hydrogenation has lagged behind,perhaps because base metals tend to engage in one-electron or radicalchemistry. Several complexes of iron, for example, were reported forcatalytic hydrogenation of ketone groups or alkene groups, but theeffectiveness of such complexes typically has been restricted to aparticular class of substrate, and such complexes are often sensitive towater and also to compounds with oxygen-containing groups and/ornitrogen-containing groups.

Complexes of cobalt may be used for homogeneous hydrogenation ofunsaturated compounds. HCo(CO)₄, Co(H)(CO)(P^(n)Bu₃)₃, and relatedcobalt(I) complexes, for example, are used for the catalytichydrogenation of alkenes and arenes at temperatures greater than 120° C.and pressures greater than 30 atm of hydrogen (“H₂”). Complexes ofcobalt with diiminopyridine ligands as well as the dinitrogen complexCo(H)(N₂)(PPh₃)₃ are used for the catalytic hydrogenation of olefins atroom temperature, and an asymmetric hydrogenation of substitutedstyrenes was recently developed. The cobalt(I) dihydrogen complex[(P(CH₂CH₂PPh₂)₃)Co(H₂)]BPh₄ was used for the catalytic hydrogenation ofcarbon dioxide (CO₂) and bicarbonates to formic acid derivatives.

Reports are scarce for catalytic hydrogenation of aldehydes and ketonesusing complexes of cobalt. Aldehyde hydrogenation was reported as a sidereaction in the catalytic hydroformylation of olefins at 185° C. withCo₂(CO)₈ and 300 atm of synthesis gas. The catalytic hydrogenation ofaldehydes using the cobalt complex Co(H)(CO)(P^(n)Bu₃)₃ with 30 atm H₂has been reported, but reaction was complicated by a competing aldehydedecarbonylation reaction. A complex of cobalt and dioxime ligand hasbeen used for the catalytic asymmetric hydrogenation of benzil, but thesubstrate scope was limited to 1,2-dicarbonyl compounds.

Nearly all prior examples of catalytic hydrogenation with complexes ofcobalt have employed cobalt(I), i.e. cobalt in the +1 oxidation state,and most of these examples have been limited in substrate scope.

There are some examples of catalytic hydrogenation with complexes ofnickel. A complex of nickel with a diphosphine-borane ligand was usedfor styrene hydrogenation at room temperature. The hydrogen activationmechanism was suggested to involve a cooperative metal-ligandinteraction in which a nickel(0) complex accepts a proton and the boronon the ligand serves as a hydride acceptor.

Caulton et al. reported a complex of nickel of the formula[(PNP′)Ni]BAr^(F) ₄ (PNP′=⁻N(SiMe₂CH₂P(^(t)Bu)₂)₂) and proposed that itcleaved H₂ heterolytically through a pathway having Ni^(IV) dihydridecharacter. The PNP ligand is sometimes referred to in the art as a“pincer” ligand. This unusual example of H₂ activation may involve aninteraction between the nickel and the nitrogen of the pincer ligandshown in Scheme 1.

These types of interactions between the metal and ligand might also beinvolved in catalytic hydrogenation of polar multiple bonds usingcomplexes of precious metals.

SUMMARY OF THE INVENTION

An aspect of the invention relates to a composition of the formula

wherein R₁ is selected independently from cycloalkyl, alkyl, substitutedalkyl, phenyl, or substituted phenyl;

wherein R₂ is selected from —CH₂Si(CH₃)₃, H, alkyl, substituted alkyl,phenyl, substituted phenyl, amido, or alkoxide;

wherein M is cobalt or nickel; and

wherein X is a counterion.

Another aspect of the invention relates to a composition of the formula

wherein R₁ is selected independently from cycloalkyl (e.g. cyclohexyl,adamantyl), alkyl, substituted alkyl, phenyl, or substituted phenyl;

wherein R₂ is —CH₂Si(CH₃)₃, H, alkyl, substituted alkyl, phenyl,substituted phenyl, alkoxide or amido; and

wherein M is cobalt or nickel.

Another aspect of the invention relates to a process for hydrogenation.The process involves combining a composition of the formula

or of the formula

wherein R₁ is selected independently from cycloalkyl, alkyl, substitutedalkyl, phenyl, or substituted phenyl;

wherein R₂ is —CH₂Si(CH₃)₃, hydrogen, or alkyl, substituted alkyl,phenyl, substituted phenyl, alkoxide, or amido;

wherein M is cobalt or nickel, and

wherein X is a counterion,

with hydrogen and an unsaturated compound under conditions effective forhydrogenation of the unsaturated compound.

DETAILED DESCRIPTION

Embodiment complexes of cobalt and of nickel were synthesized and usedfor catalytic homogeneous hydrogenation of unsaturated compounds.Embodiment cobalt complexes include cobalt in the +2 oxidation state(i.e. cobalt(II)) and the tridentate ligandsbis[2-(dialkylphosphino)ethyl]amine (HN(CH₂CH₂P(R)₂)₂ (“PNHP^(R)”, whereR=cyclohexyl, alkyl, substituted alkyl, phenyl, or substituted phenyl).These bulky ligands are sometimes referred to in the art as “pincer”ligands. The hydrogenation reactions using these embodiment cobaltcomplexes take place under relatively mild conditions. Embodimentcomplexes of nickel with the PNHP^(R) ligand were also prepared and usedfor catalytic homogeneous hydrogenation of unsaturated compounds. Someembodiment complexes that fall within the scope of this invention havethe formula

wherein R₁ is selected independently from cycloalkyl (e.g. cyclohexyl,adamantyl), alkyl, substituted alkyl, phenyl, or substituted phenyl;

wherein R₂ is —CH₂Si(CH₃)₃, H, alkyl, substituted alkyl, phenyl,substituted phenyl, alkoxide, or amido;

wherein M is cobalt or nickel; and

wherein X is a counterion. Some non-limiting examples of counterions Xinclude tetraphenylborate, hexafluorophosphate, B(C₆F₅)₄, orB(3,5-(CF₃)₂C₆H₃)₄. Other embodiment complexes that also fall within thescope of this invention have the formula

wherein R₁ is selected independently from cycloalkyl (e.g. cyclohexyl,adamantyl), alkyl, substituted alkyl, phenyl, or substituted phenyl;

wherein R₂ is —CH₂Si(CH₃)₃, H, alkyl, substituted alkyl, phenyl,substituted phenyl, alkoxide, or amido; and

wherein M is cobalt or nickel.

The embodiment cobalt complexes will be described first.

Unless specified otherwise, all reactions were carried out under a dryargon atmosphere using standard glove-box and Schlenk techniques.Deuterated solvents were purchased from CAMBRIDGE ISOTOPE LABORATORIES.Benzene-d₆ and THF-d₈ were dried over Na metal, and CD₂Cl₂ was driedover CaH₂. Anhydrous grade THF, pentane, benzene, toluene, and diethylether were obtained from ALDRICH or ACROS and stored over 4 Å molecularsieves. ¹H, ¹³C, and ³¹P NMR spectra were obtained at room temperatureon a BRUKER AV400 MHz spectrometer, with chemical shifts (δ) referencedto the residual solvent signal (¹H and ¹³C) or referenced externally toH₃PO₄ (0 ppm). GC-MS analysis was obtained using a HEWLETT PACKARD 6890GC system equipped with a HEWLETT PACKARD 5973 mass selective detector.UV-vis spectra were obtained on an AGILENT 8453 UV-visiblespectrophotometer equipped with a PELTIER thermostatted single cellholder. IR spectra were obtained on a PERKIN-ELMER SPECTRUM ONEinstrument. Elemental analyses were performed by ATLANTIC MICROLAB ofNorcross, Ga. Bis[2-(dicyclohexylphosphino)ethyl]amine (abbreviated asPNHP^(Cy)) was prepared by a previously reported procedure or purchasedfrom STREM CHEMICAL. Cyclohexene-d₁₀ was purchased from C/D/N ISOTOPES,INC. The complexes (pyr)₂Co(CH₂SiMe₃)₂ and H[BAr^(F) ₄].(Et₂O)₂ wereprepared according to previously published procedures. BArF⁴ is theabbreviation for the bis-3,5-trifluoromethyltetraphenylborate anion.Et₂O is the abbreviation for diethyl ether. “Me” is the abbreviation formethyl. “Pyr” is the abbreviation for pyridine.

Reaction of PNHP^(Cy) with (pyr)₂Co(CH₂SiMe₃)₂ afforded the paramagneticcobalt(II) complex (PNP^(Cy))Co(CH₂SiMe₃) (1) as dark yellow crystals in82% isolated yield. In the solid state, complex 1 has a square planargeometry. In solution, complex 1 exhibits a magnetic moment that isconsistent with a square planar low-spin d⁷ configuration(μ_(eff)=2.2μ_(B)). In the solution state, the magnetic moment ofcomplex 1 has a value close to 2.1μ_(B), which is the value reported for(N(SiMe₂CH₂PPh₂)₂)Co(CH₂SiMe₃), which also has a square planar geometry.This procedure was effective for the synthesis of complexes of thecomposition (PNP^(R))Co(CH₂SiMe₃) where R=cyclohexyl, alkyl, substitutedalkyl, phenyl, or substituted phenyl.

Addition of one equivalent of the known acid H[BAr^(F) ₄].(Et₂O)₂(BAr^(F) ₄=B(3,5-(CF₃)₂C₆H₃)₄) to a THF-d₈ solution of complex 1resulted in paramagnetic complex [(PNHP^(Cy))Co(CH₂SiMe₃)]BAr^(F) ₄ (2).The structural formulas of complexes 1 and 2 are shown below(Me=methyl).

Complex 2 was detected by ¹H NMR spectroscopy in 90% yield (integrationagainst an internal standard). Complex 2 was isolated in 85% yield andcharacterized by NMR and IR spectroscopy, X-ray crystallography, andelemental analysis. The ¹H NMR spectrum of complex 2 showed a broad peakat −20.88 ppm corresponding to the Si(CH₃)₃ protons on the alkyl ligand,and the IR spectrum of 2 showed an N—H stretch at 3147 cm⁻¹.

Complexes 1 and 2 were used for the catalytic hydrogenation of styrene.Hydrogenation was slow using 2 mol % of complex 1, with only about 2%conversion of styrene to ethylbenzene observed after 24 hours at 60° C.under 1 atmosphere of hydrogen (“H₂”). Hydrogenation of styrene wasfaster using complex 2; complete conversion (50 turnovers) was observedfor the hydrogenation of styrene to ethylbenzene within 2 hours at roomtemperature under just 1 atm hydrogen using 2 mol % of complex 2, whichwas generated in situ from complex 1 and H[BAr^(F) ₄].(Et₂O)₂) in THFsolution. Results were identical when an isolated sample of complex 2was used.

The hydrogenation of styrene using complex 2 was not affected by theaddition of excess Hg metal. This observation is consistent with thepresence of an active homogeneous catalyst. With a lower catalystloading (0.05 mol % complex 1 and 0.05 mol % H[BAr^(F) ₄].(Et₂O)₂), 1100turnovers were observed after 24 hours at room temperature for thehydrogenation of styrene (1 atm H₂). A variety of substrates werehydrogenated using complex 2 generated in situ by combining complex 1 (2mol %) and H[BAr^(F) ₄].(Et₂O)₂ (2 mol %) in THF (see Equation 1 below).

In the above equation, R¹ and R² are independently selected fromhydrogen, alkyl, aryl, substituted alkyl, and substituted aryl groups.The hydrogenation reaction conditions included a substrate concentrationof 0.5 millimolar in tetrahydrofuran (THF) solvent and 1 atmosphere H₂at 25° C. Results of the hydrogenation reactions are summarized in Table1 below.

TABLE 1 time yield Entry substrate product (h) (%) 1

24 100 2

24 100 3

24  99 4

24 100 5

24  99 6

24 100 7

24  99 8

24 100 9

24 100 10 

24 100 11 

40  80 12 

42  99

The yields of the hydrogenated products were determined by gaschromatography (GC). Hydrogenation of terminal alkenes such as 1-octeneand α-methylstyrene proceeded readily within 24 hours at roomtemperature with excellent yields (see Table 1, entries 5-7). Internalalkenes trans-2-octene, cis-cyclooctene, and norbornylene were alsohydrogenated at room temperature (see Table 1, entries 8-10).Hydrogenation of (R)-(+)-limonene occurred selectively at the terminalposition; the internal tri-substituted C═C bond was not hydrogenated(see Table 1, entry 11). At room temperature, hydrogenation of(+)-dihydrocarvone occurred only at the C═C bond, affording5-isopropyl-2-methylcyclohexanone in 99% yield (see Table 1, entry 12).

Complex 2 generated in situ from complex 1 (2 mol %) and H[BAr^(F)₄].(Et₂O)₂ (2 mol %) was also used for hydrogenating aldehydes, ketones,and imines (Equation 2 below).

In the above equation, R¹, R², R³, and R⁴ are independently selectedfrom hydrogen, alkyl, aryl, substituted alkyl, and substituted arylgroups. The hydrogenations of the aldehydes and ketones took place undermild conditions, which was unexpected in view of the mild reactionconditions and scarcity of reported cobalt complexes that hydrogenatealdehydes and ketones. The results for the aldehyde, ketone, and iminehydrogenations are summarized in Table 2.

TABLE 2^(a) time isolated yield (%) Entry substrate product (h) (NMRyield) 1

24 89 (98)  2^(c)

43 86 (94)  3^(c)

24 92 (98)  4^(c)

48 91 (99)  5^(c)

48 97 (99)  6^(c)

24 100^(f)  7^(d)

65  99^(f) 8

24 86 (92) 9

24  96 (100) 10^(b)

24 92 (98) 11^(b)

24 91 (99) 12^(e)

64  92 (100) 13^(e)

42 84 (89) 14^(e)

72 88 (98) 15^(e)

48 65 (70) ^(a)Conditions: substrate 0.5 mmol in THF (2 mL), 1 atm H₂,25° C. ^(b)Reactions run at 50° C. ^(c)Reactions run at 60° C.^(d)Reactions run at 25° C. under 4 atm H₂ pressure. ^(e)Reactions runat 60° C. under 4 atm H₂ pressure. ^(f)yields were determined by GC-MS.

As Table 2 shows, acetophenone (entry 1) was hydrogenated using complex2 in nearly quantitative yield within 24 hours at room temperature under1 atm of hydrogen. Several substituted acetophenone derivatives werehydrogenated at 60° C. (1 atm H₂), including 2-bromoacetophenone,3-methoxyacetophenone, and α-trifluoromethylacetophenone (86-92%isolated yields, Table 2, entries 2-4). Aliphatic ketones 2-hexanone and2-indanone were hydrogenated in high yields when the reaction was run at60° C. (1 atm H₂) for 24 hours and 48 hours, respectively (Table 2,entries 5-6). Aldehydes were also hydrogenated by in situ-generatedcomplex 2 (2 mol %). Benzaldehyde and the substituted benzaldehydes2-bromobenzaldehyde, 2-methoxybenzaldehyde, and 4-methoxybenzaldehydewere hydrogenated to the corresponding alcohols in excellent yields(86-96% isolated yields) within 24 hours under 1 atm of hydrogen (Table2, entries 8-11). The unsubstituted aliphatic aldehyde 1-octanal washydrogenated more slowly, affording 1-octanol in 92% isolated yieldafter 64 hours at 60° C. under 4 atm H₂ (Table 2, entry 12). Theeffectiveness of cobalt complex 2 in hydrogenation reactions ofaldehydes stands in contrast to the effectiveness of the known ironcomplex (PNP^(tBu))Fe(H)(CO)(Br)(PNP^(tBu)=2,6-bis(di-tert-butylphosphinomethyl)-pyridine). The ironcomplex was reported to be effective for the hydrogenation of a numberof ketones; low conversion (39%) was reported for hydrogenation ofbenzaldehyde.

Imines were hydrogenated using in situ-generated complex 2.Hydrogenation of N-benzylidene benzylamine proceeded under 4 atm H₂ at60° C. to afford dibenzylamine in 84% isolated yield using 2 mol % ofcomplex 2 (Table 2, entry 13). N-Benzylidene-methylamine andN-benzylideneaniline were also hydrogenated by the cobalt catalyst,affording N-benzyl methyl amine and N-benzylaniline in good yields(Table 2, entries 14 and 15). Previous examples of cobalt-catalyzedimine hydrogenation are scarce.

Given the broad substrate scope demonstrated, we performed furtherexperiments to assess the functional group tolerance of the cobaltcatalytic system. Table 3 summarizes the results of some experiments forassessing the functional group tolerance of complex 2. Hydrogenation ofthe alkene moiety in tert-butyl-3-butenoate was unaffected by thepresence of the ester, proceeding in high yield (99% GC yield) using insitu generated 2 (2 mol %) after 24 h at room temperature (1 atm H₂,Table 3, entry 1). Surprisingly, complex 2 catalyzed the hydrogenationof 4-pentenoic acid to afford pentanoic acid (82% isolated yield),although somewhat more forcing conditions were required (1 atm H₂, 60°C., 24 h, Table 3, entry 2). 4-Penten-1-ol was also hydrogenated inquantitative GC yield within 24 h at room temperature (1 atm H₂, Table3, entry 3). The cobalt catalyst was also active in the presence of asecondary amine, hydrogenating N-methyl-4-piperidone toN-methyl-4-piperidinol in 66% GC yield.

TABLE 3 yield Entry substrate product time (h) (%) 1

24 99  2^(a)

24 82 (99) 3

24 99  4^(a)

65 66 5

24 99

As water can be an impurity in reagents and solvents, the activity ofcomplex 2 (2 mol %) was tested in a hydrogenation reaction of styrene inthe presence of 10 mol % water added to the reaction mixture. Althoughthe hydrogenation reaction was somewhat inhibited by the water,hydrogenation proceeded to generate ethylbenzene in 99% yield after 24hours at room temperature. The ability of the cobalt complex 2 totolerate other functional groups and added water is remarkable to usbecause this behavior appears more like the behavior of complexes ofprecious metals than the behavior of complexes of base metals incatalytic hydrogenation reactions.

Additional experiments were performed to gain insight into possiblecatalytic reaction mechanisms. One atmosphere of hydrogen was added to aTHF-d₈ solution of paramagnetic cobalt(II) alkyl complex 2 and themixture was monitored by ¹H NMR spectroscopy. Within 1 hour at roomtemperature, ¹NMR signals corresponding to complex 2 disappeared fromthe ¹H NMR spectrum while a new signal at 0 ppm appeared whichcorresponded to tetramethylsilane (TMS). Although the solution had ayellow color, which might be interpreted as corresponding to thepresence of a homogeneous cobalt complex, no signals attributable tosuch a complex were observed in the ¹H NMR spectrum of the solution. Themagnetic moment (μ_(eff)) of the solution was approximately 2.7μ_(B),measured using the Evans method. This value is consistent with aparamagnetic material.

Other experiments suggested that a cobalt(II) hydride complex 3 may havebeen formed upon the reaction of cobalt(II) alkyl complex 2 withhydrogen. To test this theory, complex 2 was treated with hydrogen (1atm) in THF-d₈ solution for 3 hours, affording tetramethylsilane andcobalt product(s). Subsequent addition of CHCl₃ (2 equiv) resulted in animmediate color change from yellow to red, and the production of CH₂Cl₂(as determined by ¹H NMR spectroscopy). The cobalt product of thisreaction was isolated and identified as the cobalt(II) chloride complex[(PNHP^(Cy))Co(Cl)]BAr^(F) ₄(4) by X-ray crystallography, IRspectroscopy, and elemental analysis. The formation of chloride complex4 upon trapping with CHCl₃ implies that the hydride complex[(PNHP^(Cy))Co(H)]BAr^(F) ₄(3) was formed upon the reaction of 2 withhydrogen (see Equation 3 below).

Solutions containing complex 3 catalyzed alkene isomerization rapidly atroom temperature. When 1-octene (200 equiv) was added to a degassedTHF-d₈ solution containing complex 3, complete isomerization at roomtemperature occurred within 20 minutes to afford a mixture of internaloctenes.

Metal-hydride and π-allyl mechanisms had been commonly proposed fortransition-metal mediated olefin isomerization. In a metal-hydridecatalyzed pathway, olefin isomerization occurs via olefin insertion intothe M-H bond, followed by β-hydride elimination. In the π-allylmechanism, isomerization occurs by coordination of the olefin to an opensite at the metal, C—H activation to generate a π-allyl complex,followed by reductive elimination. Olefin dissociation then regeneratesthe open site at the metal. We performed a cross-over experiment todistinguish between these two pathways for complex 3 (see Equation 4below). In Equation 4, “d” refers to deuterium and “h” refers tohydrogen. Thus, cyclohexene-d₁₀ refers to a fully deuterated cyclohexenemolecule.

Hydrogen (H₂) was added to a mixture of complex 1 and H[BAr^(F)₄].(Et₂O)₂ in THF-d₈ and allowed to react at room temperature for 1hour. The hydrogen was removed, and then a 1:1 mixture ofcyclohexene-d₁₀ and 1-pentene was added. Within 30 minutes at roomtemperature, isomerization of the 1-pentene to 2-pentene was observed by¹H NMR spectroscopy. In addition, deuterium from the cyclohexene-d₁₀ wasscrambled into the 2-pentene and resonances corresponding tocyclohexene-d_(10-n)-h_(n) grew into the NMR spectrum, consistent with apathway for isomerization involving a discreet metal-hydrideintermediate. No deuterium exchange would be expected for the π-allylmechanism.

Few examples of isolable cobalt(II) hydride complexes have beenreported, and little is known about their reactivity. Cationiccobalt(II) hydride complexes [Co(H)(L)₄]⁺ (L=P(OEt)₂Ph, P(OPh)₃) havebeen prepared by oxidation of their neutral cobalt(I) analogues. Hydridecomplex [(triphos)Co(PEt₃)H]BPh₄ (triphos=CH₃C(CH₂PPh₂)₃) has beenstructurally characterized but only limited reactivity studies have beenperformed with it. The trapping and crossover experiments presentedabove suggest the involvement of the cobalt(II) hydride complex[(PNHP^(Cy))Co(H)]BAr^(F) ₄ in the hydrogenation reactions.

Without wishing to be bound by any theory or explanation, we propose acatalytic cycle in Scheme 2 below for the observed catalytichydrogenation using complexes of cobalt and PNHP^(Cy).

As Scheme 2 shows, hydrogenolysis of the cobalt(II) complex 2 generatescobalt(II) complex 3 and tetramethylsilane. Alkene insertion into theCo—H bond would afford a cobalt(II) alkyl intermediate, which could thenreact further with hydrogen to release product and turnover thecatalyst.

Another possible explanation is that a small amount of a highly activecobalt(I) hydride complex is formed instead. We have been unable toindependently prepare such a complex.

Details related to the synthesis of several non-limiting embodiments ofcomplexes of cobalt and PNP^(Cy), PNHP^(Cy), as well as severalnon-limiting hydrogenation reactions, are provided in the EXAMPLESbelow.

Examples with Complexes of Cobalt

Synthesis of (PNP^(Cy))Co(CH₂SiMe₃) (1). In a small vial, PNHP^(Cy)(71.0 milligrams (“mg”), 0.153 millimoles (“mmol”)) and(pyridine)₂Co(CH₂SiMe₃)₂(61.0 mg, 0.156 mmol) were dissolved in toluene(2 mL) to form a dark green solution. After standing for 20 minutes, thecolor changed from dark green to yellow-brown. The solvent was removedunder vacuum. The residue was dissolved in diethylether (1 milliliter(“mL”) and the resulting solution was cooled to −20° C. overnight, whichafforded yellow-brown crystals of complex 1. The supernatant was removedby pipette and the crystals were dried under vacuum. Yield: 78 mg (82%).¹H NMR (400 MHz, THF-d₈) δ 6.55 (br, 2H), 3.38 (br, 8H), 2.69 (br, 8H),2.00 (br, 6H), 1.62 (br, 4H), 1.29 (br, 6H), 1.12 (br, 6H), 0.89 (br,6H), 0.22 (br, 6H), −5.26 (br, 9H, Si(CH₃)₃). UV-vis: 286 nm (ε=1580 M⁻¹cm⁻¹), 348 nm (ε=1060 M⁻¹ cm⁻¹), 428 nm (ε=380 M⁻¹ cm⁻¹).μ_(eff)=2.2μ_(B). Anal. Calcd for C₃₂H₆₃CoNP₂Si: C, 62.92; H, 10.40; N,2.29. Found: C, 62.77; H, 10.24; N, 2.13.

Synthesis of (PNP^(Ph))Co(CH₂SiMe₃). In a vial,bis(diphenylphosphino)ethylamine (74 mg, 0.18 mmol) was dissolved intoluene (2 mL). To the toluene solution was added a solution of(pyr)₂Co(CH₂SiMe₃)₂ (62 mg, 0.16 mmol) in toluene (2 mL). The reactionmixture turned a red color. The toluene was removed under vacuum, andthe red residue was dissolved in diethyl ether (3 mL), and filteredthrough a plug of celite. The solvent was removed under vacuum,affording a dark red oil. Yield: 64 mg (68%). ¹H NMR (400 MHz,benzene-d₆) δ 8.80 (br), 7.50 (br), 7.13 (br), 6.28 (br), −4.54 (br).

Synthesis of (PNP^(Ad))Co(CH₂SiMe₃). In a small vial,(pyr)₂Co(CH₂SiMe₃)₂ (44 mg, 0.11 mmol) andbis(diadamantylphosphino)ethylamine (75 mg, 0.11 mmol) were combined intoluene (1 mL). The solution was allowed to stand at room temperaturefor 3 hours, during which time the color changed from green to anorange-brown. The solvent was removed under vacuum, and then diethylether (1 mL) was added to the orange-brown solid. The suspension wascooled to −20° C. overnight. The supernatant was removed by pipette, andthe orange solid dried under vacuum. Yield: 74 mg (81%). ¹H NMR (400MHz, THF-d₈) δ 6.05 (br), 2.33 (br), 1.99 (br), 1.86 (br), 1.12 (br),−5.73 (br).

Synthesis of (PNP^(iPr))Co(CH₂SiMe₃). In a vial,bis(diisopropylphophino)ethylamine (66 mg, 0.21 mmol) and(pyr)₂Co(CH₂SiMe₃)₂ (84 mg, 0.21 mmol) were dissolved in toluene (4 mL).The solution turned a yellow-brown color. The reaction mixture wasallowed to stand at room temperature for 10 minutes, and then thesolvent removed under vacuum, affording a yellow-brown oil. Yield: 86 mg(88%). ¹H NMR (400 MHz, benzene-d₆) δ 1.98 (br), 0.63 (br), −4.91 (br).

Synthesis of [(PNHP^(Cy))Co(CH₂SiMe₃)]BAr^(F) ₄ (2). In a small vial,complex 1 (6.1 mg, 10 micromoles (“μmol”) and H[BAr^(F) ₄].(Et₂O)₂ (10.1mg, 10 μmol) were dissolved in diethyl ether (0.5 mL). The resultingsolution was layered carefully with pentane (1.0 mL) and the vial wassealed and then cooled to −25° C. for three days, during which timeyellow plates formed. The supernatant was removed by pipette, and thenthe crystals were washed with pentane (1 mL) and dried under vacuum.Yield: 12.5 mg (85%). ¹H NMR (400 MHz, THF-d₈) δ 16.16 (br, 2H,PNHP^(Cy)), 15.43 (br, 2H, PNHP^(Cy)), 7.72 (s, 8H, BAr^(F) ₄), 7.51 (s,4H, BAr^(F) ₄), 6.06 (br, 2H, PNHP^(Cy)), 5.72 (br, 2H, PNHP^(Cy)), 4.54(br, 2H, PNHP^(Cy)), 4.09 (br, 2H, PNHP^(Cy)), 3.07 (br, 2H, PNHP^(Cy)),2.69 (br, 2H, PNHP^(Cy)), 1.54 (br, 2H, PNHP^(Cy)), 1.30 (br, 6H,PNHP^(Cy)), −0.59 (br, 2H, PNHP^(Cy)), −1.64 (br, 2H, PNHP^(Cy)), −20.88(s, 9H, Si(CH₃)₃). UV-vis: 354 nm (ε=2500 M⁻¹ cm⁻¹), 444 nm (ε=310 M⁻¹cm⁻¹). μ_(eff)=2.8μ_(B). IR (thin film): v_(N—H)=3147 cm⁻¹. Anal. Calcdfor C₆₄H₇₆BCoF₂₄NP₂Si: C, 52.11; H, 5.19; N, 0.95. Found: C, 52.13; H,5.34; N, 0.94.

Synthesis of [(PNHP^(Cy))Co(Cl)]BAr^(F) ₄ (4). In an NMR tube equippedwith a resealable TEFLON stopper, complex 1 (4.4 mg, 7.2 μmol) andH[BAr^(F) ₄].(Et₂O)₂ (7.3 mg, 7.2 μmol) were dissolved in THF-d₈ (0.4mL). An ¹H NMR spectrum of the resulting solution revealed formation ofcomplex 2. The solution was subjected to one cycle of freeze-pump-thaw,and then H₂ (1 atm) was added. A ¹H NMR spectrum of the solution threedays later revealed that the signals corresponding to complex 2 haddisappeared and a new signal at 0 ppm had appeared (corresponding totetramethylsilane). CHCl₃ (1 μL, 0.013 mmol) was added, resulting in animmediate color change from yellow to red. Examination of the ¹H NMRspectrum revealed formation of CH₂Cl₂. Following an analogous procedureon a larger scale (10 μmol) allowed for isolation of complex 4 as redblocks by crystallization (layering a toluene/diethyl ether solutionwith pentane and cooling to −25° C.). The supernatant was removed bypipette, and the red crystals were washed with pentane and dried undervacuum. Yield: 11.0 mg (77%). ¹H NMR (400 MHz, THF-d₈). UV-vis: 410 nm(ε=510 M⁻¹ cm⁻¹), 510 nm (ε=350 M⁻¹ cm⁻¹), 705 nm (ε=110 M⁻¹ cm⁻¹).μ_(eff)=2.4μ_(B). IR (thin film): v_(N—H)=3104 cm⁻¹. Anal. Calcd forC₆₀H₆₅BClCoF₂₄NP₂: C, 50.63; H, 4.60; N, 0.98. Found: C, 49.82; H, 4.63;N, 1.09.

General procedure for C═C bond hydrogenation reactions. In a typicalexperiment, complex 1 (6.1 mg, 10 μmol) and H[BAr^(F) ₄].(Et₂O)₂ (10.1mg, 10 μmol) were dissolved in tetrahydrofuran (“THF”, 2.0 mL) in a 100mL thick-walled glass vessel equipped with a TEFLON stopcock and a stirbar. The substrate (0.5 mmol) to be hydrogenated was added and thenhexamethylbenzene (ca. 32 mg, 0.2 mmol) was added as an internalstandard. The reaction vessel was degassed by freeze-pump-thaw, 1 atm ofhydrogen gas was admitted, and the vessel was sealed. The resultingsolution was stirred at 25° C. for the indicated reaction time. At theend of the reaction time, the reaction vessel was opened under air, thereaction mixture was diluted with dichloromethane, and the yield wasdetermined by GC analysis (integration against the internal standard).Product identities were verified by GC-MS analysis and comparison toauthentic samples.

General procedure for the C═O and C═N bond hydrogenation reactions. In atypical experiment, complex 1 (6.1 mg, 10 μmol) and H[BAr^(F) ₄].(Et₂O)₂(10.1 mg, 10 μmol) were dissolved in THF (2.0 mL) in a 100 mLthick-walled glass vessel equipped with a TEFLON stopcock and a stirbar. The substrate (0.5 mmol) to be hydrogenated was then added. Thevessel was degassed by freeze-pump-thaw and then hydrogen (1 or 4 atm)was added. The resulting solution was stirred at the desired temperature(25-60° C.) for the indicated reaction time. At the end of the reaction,the solvent was evaporated and the residue was passed through silica gelin a pipette. The solvent was removed under vacuum and the ¹H NMRspectrum of the crude product mixture was recorded in CDCl₃.Hydrogenation products were then isolated by column chromatography orpreparative thin layer chromatography (“TLC”) using n-hexane/ethylacetate (3:1, v/v) as an eluent. Isolated products were characterized by¹H NMR and GC-MS, with spectra matching those reported in the literatureor authentic samples.

Hydrogenation with added Hg. Under nitrogen, complex 1 (6.1 mg, 10.0μmol) and H[BAr^(F) ₄].(Et₂O)₂ (10.1 mg, 10.0 μmol) were dissolved inTHF (2.0 mL) in a thick-walled glass vessel equipped with a TEFLONstopper and a stir bar. Styrene (52.0 mg, 0.5 mmol) and Hg (606 mg, 3mmol) were then added and hexamethylbenzene (0.1 mmol) was also added asinternal standard. The bottle was degassed by freeze-pump-thaw andcharged with 1 atm of hydrogen gas. The resulting solution was stirredat 25° C. for 24 hours, after which time the reaction mixture wasexposed to air and diluted with dichloromethane. GC analysis revealedquantitative conversion to ethylbenzene.

Hydrogenation with added water. Complex 1 (6.1 mg, 10.0 μmol) andH[BAr^(F) ₄].(Et₂O)₂ (10.1 mg, 10.0 μmol) were dissolved in a degassedmixture of THF/H₂O (2.0 mL THF containing H₂O (0.9 μL, 50 μmol)) in athick-walled glass vessel equipped with a TEFLON stopcock. Styrene (52.0mg, 0.5 mmol) was then added and hexamethylbenzene (0.1 mmol) was alsoadded as internal standard. The vessel was degassed by freeze-pump-thawand charged with 1 atm of hydrogen gas. The resulting solution wasstirred at 25° C. for 24 hours, after which time it was exposed to airand diluted with dichloromethane. GC analysis revealed that the yield ofethylbenzene was 99%.

Procedure for the hydrogenation of styrene using 0.05 mol % catalyst.Complex 1 (6.1 mg, 10.0 μmol) and H[BAr^(F) ₄].(Et₂O)₂ (10.1 mg, 10.0μmol) were dissolved in THF (10 mL) in a 100 mL thick-walled glassvessel bottle equipped with TEFLON stopcock and a stir bar. Styrene(2.08 g, 20.0 mmol) was then added and hexamethylbenzene (6.0 mmol) wasalso added as internal standard. The bottle was degassed byfreeze-pump-thaw and then charged with 1 atm of hydrogen gas (“H₂”). Theresulting solution was stirred at 25° C. for 28 hours, during which timethe reaction bottle was periodically recharged with 1 atm H₂ to continueto the reaction. After 28 hours at room temperature, the reactionmixture was exposed to air and diluted with dichloromethane, and GCanalysis revealed that the yield of ethylbenzene was 55% with a totalturnover number (TON) of 1100.

Isomerization of 1-octene. In an NMR tube equipped with a resealableTEFLON screw cap, complex 1 (3.8 mg, 6.2 μmol) and H[BAr^(F) ₄].(Et₂O)₂(6.3 mg, 6.2 μmol) were dissolved in THF-d₈ (0.4 mL). After recording aninitial ¹H NMR spectrum of the solution, the solution was degassed byfreeze-pump-thaw, and then hydrogen (1 atm) was added), and then thereaction mixture was allowed to stand at room temperature for 1 hour,after which time signals corresponding to in situ generated 2 haddisappeared from the ¹H NMR spectrum and a new signal appeared at 0 ppm,corresponding to tetramethylsilane. The hydrogen was removed bysubjecting the solution to three consecutive cycles of freeze-pump-thaw,and then 1-octene (194 μL, 1.2 mmol) was added under argon. A ¹H NMRspectrum was recorded immediately after adding the 1-octene. After 20minutes at room temperature, a ¹H NMR spectrum was recorded and thesignals from the vinylic hydrogens from 1-octene had disappeared whilenew signals from the olefinic protons from the internal octene isomershad appeared.

Cross-over experiment. In an NMR tube equipped with a resealable TEFLONscrew cap, complex 1 (6.1 mg, 10.0 μmol) and H[BAr^(F) ₄].(Et₂O)₂ (10.1mg, 10.0 μmol) were dissolved in THF-d₈ (0.6 mL). An initial ¹H NMRspectrum of the resulting solution was recorded, after which thesolution was degassed by freeze-pump-thaw, and then H₂ (1 atm) wasadded). After 1 hour at room temperature, the signals from in situgenerated complex 2 disappeared from the ¹NMR spectrum of the solutionwhile a new signal appeared at 0 ppm, corresponding totetramethylsilane. The hydrogen was removed after three consecutivecycles of freeze-pump-thaw. In a second NMR tube equipped with aresealable TEFLON screw cap, 1-pentene (14.0 mg, 0.20 mmol),cyclohexene-d₁₀ (18.4 mg, 0.2 mmol) and p-xylene (28.6 mg, 0.29 mmol,internal standard) were dissolved in THF-d₈ (0.4 mL) under argon. Aninitial ¹H NMR spectrum was recorded of the substrate mixture and theinternal standard, and then the two NMR solutions were mixed underargon. ¹H NMR spectra were recorded at room temperature after 5 min, 30min, 1 hour, 4 hours and 68 hours. Examination of the ¹H NMR spectrarevealed that complete isomerization of the 1-pentene to 2-penteneoccurred within 30 minutes at room temperature. Deuterium from thecyclohexene-d₁₀ was scrambled into the 2-pentene (resonancescorresponding to 2-pentene diminished, as judged by integration againstthe internal standard) and resonances corresponding tocyclohexene-d_(10-n)-h_(n) grew into the NMR spectrum. The presence ofprotio-cyclohexene was confirmed by comparison with an authenticcyclohexene sample.

Parallel experiments: Impact of temperature and pressure on acetophenonehydrogenation. For three parallel reactions, complex 1 (6.1 mg, 10.0μmol) and H[BAr^(F) ₄].(Et₂O)₂ (10.1 mg, 10.0 μmol) were dissolved inTHF (2.0 mL) in a thick-walled glass vessel equipped with a Teflonstopcock and a stir bar. Acetophenone (60 mg, 0.5 mmol) was then addedand hexamethylbenzene (0.1 mmol) was also added as internal standard.The reaction mixture was degassed by freeze-pump-thaw and charged with 1atm (or 4 atm) of hydrogen gas. The resulting solution was stirred at25° C. or 60° C. for 4 hours (see Equation 5), and then stopped in orderto compare relative reaction rates.

In each case, the solvent was evaporated and the residue was passedthrough silica gel in a pipette (CH₂Cl₂ as an eluent), the crude productwas evaporated to dryness and the ¹H NMR spectra recorded in CDCl₃. Theyields of 1-phenylethanol were determined by integration of the ¹H NMRspectra against the internal standard. Table 4 below shows results ofthe parallel experiments.

TABLE 4 Entry H₂/atm T/° C. NMR yield (%) 1 1 25 14 2 1 60 25 3 4 25 27

Table 5 summarizes data from additional reactions that were performed toexplore the scope of hydrogenation reactions.

TABLE 5 isolated yield (%) Entry substrate product time (h) (NMR yield)1^(b)

22 (80%) 2^(b)

24 (93%) 3 

48  95% (100%) 4^(c)

45 93% (99%) 5^(c)

45 98% (99%) 6^(c)

48 97% (99%)

It is believed that ability to hydrogenate multiple classes ofsubstrates and broad functional group tolerance makes these embodimentcobalt complexes a significant advance over previously reported earthabundant metal complexes for catalytic hydrogenation.

Turning now to nickel complexes, it should be mentioned that squareplanar complexes [(PNHP^(iPr))Ni(Br)]Br and[(PNHP^(iPr))Ni(NCCH₃)](BF₄)₂ have reported; the latter complex[(PNHP^(iPr))Ni(NCCH₃)](BF₄)₂ was found to catalyze the nucleophilicaddition of piperidine to acetonitrile.

Embodiment complexes of nickel, like the embodiment cobalt complexes,may be used for catalytic hydrogenation. Embodiment complexes of nickelsimilar to those of the cobalt complexes were prepared and used forcatalytic alkene hydrogenation under mild conditions. Experiments wereperformed to gain insight into the hydrogenation mechanism.

Reaction of PNHP^(Cy) with Ni(diglyme)Br₂ in THF, followed byrecrystallization, afforded the cationic Ni(II) complex[(PNHP^(Cy))Ni(Br)]Br (5) as orange crystals in good yield. Complex 5was characterized by NMR and IR spectroscopy and elemental analysis.Reaction of complex 5 with NaBH₄ in methanol produced[(PNHP^(Cy))Ni(H)]BPh₄ (6) (see Scheme 3 below).

The ¹H NMR spectrum (CD₃CN) of complex 6 shows a triplet hydride signalat −19.59 ppm (J_(P—H)=62.2 Hz), and the IR spectrum shows a Ni—Hstretch at 1886 cm⁻¹. The hexafluorophosphate derivate[(PNHP^(Cy))Ni(H)]PF₆ (6-PF₆) was prepared by using an analogousprocedure (vide infra) and displays very similar NMR features. The X-raystructure of complex 6-PF₆ was obtained. The distance between the nickeland the central nitrogen of the pincer ligand (1.978(2) Å) is consistentwith the nitrogen being protonated.

The neutral hydride complex (PNP^(Cy))Ni(H) (7) was prepared bydeprotonation complex 6 with KH (see Scheme 4). In the ¹H NMR spectrumof complex 7 (benzene-d₆), the hydride signal appears as a triplet at−17.32 ppm (J_(P—H)=62.8 Hz), shifted more than 2 ppm downfield from thehydride signal of complex 6. The IR spectrum of complex 7 shows a Ni—Hstretch at 1811 cm⁻¹. Single crystals of complex 7 were grown from aconcentrated diethyl ether solution. A single crystal X-ray diffractionstructure of complex was also obtained. The distance between the nickeland the central nitrogen of the pincer ligand of complex 7 (1.876(2) Å)is significantly shorter than the Ni—N distance of complex 6 (1.978(2)Å).

Cationic complex 6 and neutral complex 7 were evaluated for catalytichydrogenation.

Turning first to complex 6, heating styrene under hydrogen (1 atm) withcomplex 6 (10 mol %) in THF-d₈ solution produced ethylbenzene in about10% yield after 5 days at 80° C. Increasing the hydrogen pressure to 4atm resulted in complete conversion of styrene to ethylbenzene after 24hours at 80° C. (Scheme 4 and Table 6, entry 1). At the end of thereaction, the only nickel species detected in the solution by ¹H and ³¹PNMR spectroscopy was complex 6.

To test for the possible formation of an active colloidal ornanoparticle Ni catalyst, the hydrogenation of styrene using complex 6(10 mol %) was conducted with stirring in the presence of excess Hgmetal (390 equiv). The hydrogenation of styrene was unaffected by theaddition of Hg, suggesting that the active catalytic species ishomogeneous. The hydrogenation reaction mixtures maintained a clear,pale yellow appearance throughout the reaction, with no evidentformation of nickel metal.

TABLE 6^([a]) Entry Substrate Product Time (hours) Yield (%)^([b]) 1

24 100  2

24 70 3

48 97 4

48 48 5

24  5 6

24 10 ^([a])Conditions: 80° C., 4 atm H₂, THF-d₈ solvent. ^([b])Yieldswere determined by ¹H NMR spectroscopy (integration against an internalstandard) and verified by GC-MS.

Complex 6 was also tested for the hydrogenation of several othersubstrates. Heating 1-octene with complex 6 (10 mol %) under 4 atm H₂(THF-d₈ solvent, 80° C., 24 hours) produced n-octane (70%) and internaloctene isomers (30%, arising from isomerization of the 1-octene) (Table6, entry 2). Prolonging the reaction time to 48 hours resulted in ahigher yield (76%) of n-octane. Internal octene isomers (24%) remainedat the end of the reaction, indicating that the terminal 1-octene ishydrogenated more rapidly than its internal isomers. The more stericallyhindered olefins 3,3-dimethyl-1-butene and α-methylstyrene were alsohydrogenated under the same reaction conditions (4 atm H₂, 80° C.),albeit somewhat more slowly, affording neohexane (97%) andisopropylbenzene (48%) after 48 hours (Table 6, entries 3 and 4).

Lower conversions resulted from hydrogenation of aldehyde substratesusing complex 6. Heating a THF-d₈ solution of 3,5-dimethoxybenzaldehydeunder 4 atm H₂ with complex 6 (10 mol %) afforded3,5-dimethoxybenzylalcohol in 5% yield (Table 6, entry 5). The identityof the 3,5-dimethoxybenzylalcohol was confirmed by spiking the reactionmixture with the authentic compound. 3,5-Dimethoxybenzoic acid was notdetected in the reaction mixture by ¹H NMR spectroscopy, suggesting thatthe 3,5-dimethoxybenzyl alcohol was formed from the hydrogenation of thealdehyde, and not by aldehyde disproportionation. When the hydrogenationof cinnamaldehyde was performed under the same reaction conditions (4atm H₂, 80° C., 24 hours), 3-phenyl-1-propanol was formed in 10% yield(Table 6, entry 6).

We believe that the reactions above, which relate to hydrogenation ofC═O and C═C groups that involve complex 6, are unusual because of therelatively mild reaction conditions.

Turning now to complex 7, heating a benzene-d₆ solution of styrene under4 atm H₂ with complex 7 (10 mol %) resulted in a 30% yield ofethylbenzene after 24 hours at 80° C. A somewhat higher conversion wasobserved in the hydrogenation of 1-octene using 7 (10 mol %), whichafforded a mixture of n-octane (76%) and internal octene isomers (24%)after 24 hours at 80° C. No hydrogenation of 3,5-dimethoxybenzaldehydeor cinnamylaldehyde was observed using complex 7.

Experiments were performed to try to understand the reaction mechanismfor hydrogenation using complex 6. For example, addition of excess of1-octene to a benzene-d₆ solution of 6-PF₆ resulted in completeconversion to the complex [(PNHP^(Cy))Ni(CH₂(CH₂)₆CH₃)]PF₆ (8-PF₆) after4 days at 25° C. (Scheme 5).

Complex 8-PF₆ was isolated and characterized by NMR and IR spectroscopy.The ¹³C{¹H} NMR spectrum of 8-PF₆ included a triplet (J_(P—C)=21 Hz) at−2.2 ppm for the carbon bound to the Ni center. The DEPT-135 NMRspectrum of 8-PF₆ confirmed a 1,2-insertion of 1-octene into the Ni—Hbond of 2-PF₆. The preference for a 1,2-insertion rather than a2,1-insertion are likely due to steric interactions between 1-octenewith the bulky cyclohexyl-substituted phosphines from the pincer ligand.

Insertion of 1-octene into the Ni—H bond of 6 was found to bereversible. An isolated sample of complex 8-PF₆ was heated in benzene-d₆solution (80° C.) in the absence of 1-octene to afford complex 6-PF₆(80%), 1-octene (47%), and internal octene isomers (30%). An isolatedsample of complex 8 was heated in THF-d₈ solution under hydrogen (4atm). After 2 hours at 80° C., 90% conversion of complex 8 had occurred,affording complex 6, 1-octene (64%), and n-octane (25%). Besides showingthe reversibility of the insertion, the above results also suggest that6-hydride elimination occurs more rapidly than alkane product releasefrom complex 8.

The deuteride complex [(PNDP^(Cy))Ni(D)]PF₆ (6-d₂) was prepared, and abenzene-d₆ solution of 6-d₂ was treated with H₂ (1 atm). H-D gas wasdetected by ¹H NMR spectroscopy within 10 minutes at room temperature(Scheme 6), and the resonances corresponding to the Ni—H and N—H grewinto the ¹H NMR spectrum of complex 6 over the course of 24 hours (25°C.).

The formation of the H-D gas suggests a reaction mechanism in which H₂gas adds to the cationic nickel(II) center of 6-d₂, as opposed to amechanism involving elimination of D₂ from 6-d₂ followed by reactionwith H₂, which would not be expected to form H-D.

Treatment of complex 6 with 50 equivalents of styrene resulted inapproximately 85% conversion to the insertion product[(PNHP^(Cy))Ni(CH₂CH₂Ph)]BPh₄ (9), which was identified by its ¹H,¹³C{¹H}, and DEPT-135 NMR spectra (THF-d₈) recorded in the presence ofexcess styrene. The ¹³C{¹H} NMR spectrum of 9 generated in situ showed atriplet signal for the carbon bound to the nickel center at 0.35 ppm(J_(P—C)=20 Hz). By contrast, when a THF-d₈ solution of complex 6 and 10equivalents of 3,5-dimethoxybenzaldehyde was heated at 80° C. for 24hours, no apparent reaction had occurred.

Details related to the synthesis of several non-limiting embodiments ofcomplexes of nickel as well as several non-limiting embodimenthydrogenation reactions are provided in the EXAMPLES below. Unlessspecified otherwise, all reactions were carried out under a dry argonatmosphere using standard glove-box and Schlenk techniques. Deuteratedsolvents were purchased from CAMBRIDGE ISOTOPE LABORATORIES. Benzene-d₆and THF-d₈ were dried over Na metal, CD₃CN and CD₂Cl₂ were dried overCaH₂, and CDCl₃ was used as received. 1-Octene was dried over sodiummetal, and styrene was dried over CaH₂. Anhydrous grade THF, pentane,benzene, toluene, and diethyl ether were obtained from ALDRICH or ACROSand stored over 4 Å molecular sieves.Bis[2-(dicyclohexylphosphino)ethyl]amine was purchased from STREMCHEMICAL, and nickel(II) bromide 2-methoxyethyl ether complex(Ni(diglyme)Br₂) was purchased from ALDRICH. ¹H, ¹³C, and ³¹P NMRspectra were obtained at room temperature on a BRUKER AV400 MHzspectrometer, with chemical shifts (δ) referenced to the residualsolvent signal (¹H and ¹³C) or referenced externally to H₃PO₄ (0 ppm).GC-MS analysis was obtained using a Hewlett Packard 6890 GC systemequipped with a HEWLETT PACKARD 5973 mass selective detector. Elementalanalyses were performed by ATLANTIC MICROLAB (Norcross, Ga.).

Examples with Complexes of Nickel

Synthesis of [(PNHP^(Cy))Ni(Br)]Br (5). In a vial, PNHP^(Cy) (91.5 mg,0.197 mmol) and Ni(diglyme)Br₂ (65.0 mg, 0.185 mmol) were combined inTHF (4 mL), and the orange reaction mixture was stirred for 18 hours atroom temperature. Methanol (3 mL) was added, and then the mixture wasfiltered through a TEFLON syringe filter. The filter was washed withmethanol (2 mL), the solution and filtrate were combined, and thesolvent removed under vacuum. The resulting orange residue wasrecrystallized from methylene chloride/diethyl ether, affording orangecrystals of complex 6. The crystals were washed with diethyl ether (2×3mL), and dried under vacuum. Yield of complex 5: 117 mg (87%). ¹H NMR(400 MHz, CDCl₃) δ 6.90 (br s, 1H, NH), 3.21-3.12 (m, 2H, PNP),2.46-2.43 (m, 2H, PNP), 2.35-2.16 (m, 10H, PNP), 2.04-1.89 (m, 14H,PNP), 1.82-1.58 (m, 12H, PNP), 1.43-1.28 (m, 12H, PNP). ¹³C{¹H} NMR (100MHz, CDCl₃): 54.8 (vt, J_(P—C)=5 Hz), 34.3 (vt, J_(P—C)=11 Hz), 33.5(vt, J_(P—C)=12 Hz), 29.5 (s), 28.5 (s, 2C), 28.4 (s), 27.4-26.8 (m,4C), 26.2 (s), 26.0 (s), 21.9 (vt, J_(P—C)=9 Hz). ³¹P{¹H} NMR (162 MHz,CDCl₃): 49.0 (s). IR (thin film): v_(N—H)=3402 cm⁻¹. Anal. Calcd forC₂₈H₅₃Br₂NNiP₂: C, 49.15; H, 7.81; N, 2.05. Found: C, 49.61; H, 7.89; N,1.96.

Synthesis of [(PNHP^(Cy))Ni(H)]BPh₄ (6-BPh₄). In a vial, complex 5 (54.0mg, 0.0818 mmol) was dissolved in methanol (8 mL) by stirring at roomtemperature. A total of 15.3 mg NaBH₄ (15.3 mg, 0.403 mmol) was added intwo portions to the solution. The solution changed color from orange toa lighter yellow color and bubbled vigorously. In a separate vial,NaBPh₄ (32.6 mg, 0.0953 mmol) was dissolved in methanol (1 mL). Once thebubbling subsided, the solution of NaBPh₄ was carefully layered on topof the reaction mixture, and allowed to stand at room temperature for 2hours, during which time light golden-colored crystals formed. Thesupernatant was removed by pipette and the crystals washed with diethylether (2×3 mL) and dried under vacuum. Yield of complex 6-BPh₄: 60.9 mg(84%). ¹H NMR (400 MHz, CD₃CN) δ 7.29-7.25 (m, 8H, BPh₄), 6.99 (t, 8H,J=7.2 Hz, BPh₄), 6.84 (t, 4H, J=7.2 Hz, BPh₄), 3.90 (br s, 1H, NH),3.25-3.11 (m, 2H, PNP), 2.41-2.31 (m, 2H, PNP), 2.19-2.00 (m, 6H, PNP),1.99-1.69 (m, 20H, PNP), 1.48-1.18 (m, 22H, PNP), −19.59 (t, 1H,J_(P—H)=62.2 Hz, Ni—H). ¹³C{¹H} NMR (100 MHz, CD₃CN): 164.9 (q,J_(B—C)=49 Hz), 136.8 (s), 126.7 (q, J_(B—C)=3 Hz), 122.9 (s), 52.2 (vt,J_(P—C)=4 Hz), 34.3 (vt, J_(P—C)=12 Hz), 33.5 (vt, J_(P—C)=14 Hz), 30.8(s), 30.7 (s), 29.8 (s), 27.6-27.2 (m, 4C), 26.9 (s), 26.8 (s), 24.8(vt, J_(P—C)=9 Hz). ³¹P{¹H} NMR (162 MHz, CD₃CN): 56.4 (s). IR (thinfilm): v_(N—H)=3187 cm⁻¹, v_(Ni—H)=1886 cm⁻¹. Anal. Calcd forC₅₂H₇₄BNNiP₂: C, 73.95; H, 8.83; N, 1.66. Found: C, 74.02; H, 8.92; N,1.71.

Synthesis of [(PNHP^(Cy))Ni(H)]PF₆ (6-PF₆). In a small vial, complex 5(36 mg, 0.052 mmol) and NaBH₄ (12 mg, 0.32 mmol) were suspended in THF(3 mL). Methanol (1 mL) was added dropwise until the suspension began tobubble vigorously. The pale yellow mixture was allowed to react at roomtemperature for 20 minutes, during which time the bubbling ceased. Atthis time, KPF₆ (16 mg, 0.087 mmol) was added, and the reaction mixturestirred for 10 minutes. The solvent was removed under vacuum, leaving anoff-white residue. The residue was extracted with benzene (2×2 mL), andfiltered through a glass wool pipette. The benzene was removed undervacuum, leaving a nearly colorless residue. Yield of complex 6-PF₆: 28mg (80%). Crystals suitable for X-ray diffraction were obtained bydiffusion of diethyl ether into a toluene solution of 6-PF₆ at −20° C.¹H NMR (400 MHz, benzene-d₆) δ 4.32 (br s, 1H, NH), 3.21-3.12 (m, 2H,PNP), 2.46-2.43 (m, 2H, PNP), 2.35-2.16 (m, 10H, PNP), 2.04-1.89 (m,14H, PNP), 1.82-1.58 (m, 12H, PNP), 1.43-1.28 (m, 12H, PNP), −19.36 (t,1H, J_(P—H)=61.2 Hz, Ni—H). ¹³C{¹H} NMR (100 MHz, benzene-d₆): 52.6 (vt,J_(P—C)=5 Hz), 34.1 (vt, J_(P—C)=13 Hz), 33.4 (vt, J_(P—C)=14 Hz), 30.5(s), 30.0 (s), 29.3 (s), 28.8 (s), 27.4-27.0 (m, 4C), 26.7 (s), 26.5(s), 24.4 (vt, J_(P—C)=9 Hz). ³¹P{¹H} NMR (162 MHz, benzene-d₆): 55.2(s), −142.6 (h, J_(F—P)=713 Hz). IR (thin film): v_(N—H)=3232 cm⁻¹,v_(Ni—H)=1886 cm⁻¹.

Synthesis of (PNP^(Cy))Ni(H) (7). To a 15 mL thick-walled glass tube wasadded 6-BPh₄ (15 mg, 0.018 mmol) and KH (11 mg, 0.274 mmol). The solidswere suspended in toluene (7 mL), the vessel sealed, and the mixturestirred at 80° C. for 15 hours. The resulting brown suspension wasfiltered through a PTFE syringe filter and the toluene removed undervacuum, affording a dark yellow oil. Yield of complex 7: 7.5 mg (80%).¹H NMR (400 MHz, benzene-d₆) δ 3.48-3.40 (m, 4H, PNP), 2.18-2.14 (m, 4H,PNP), 2.04-2.00 (m, 4H, PNP), 1.90-1.68 (m, 20H, PNP), 1.62-1.12 (m,20H, PNP), −17.32 (t, 1H, J_(P—H)=62.8 Hz, Ni—H). ¹³C{¹H} NMR (100 MHz,benzene-d₆): 59.7 (vt, J_(P—C)=7 Hz), 34.9 (vt, J_(P—C)=12 Hz), 30.5(vt, J_(P—C)=2 Hz), 29.2, 27.8-27.6 (m, 2C), 27.4 (vt, J_(P—C)=9 Hz),27.1. ³¹P{¹H} NMR (162 MHz, benzene-d₆): 73.8 (s). IR (thin film):v_(Ni—H)=1811 cm⁻¹.

Isolation of [(PNHP^(Cy))Ni(CH₂(CH₂)₆CH₃)]PF₆ (8-PF₆). Complex 6-PF₆(8.4 mg, 0.013 mmol) was dissolved in benzene-d₆ (0.6 mL). 1-Octene(0.050 g, 0.45 mmol) was added and the resulting solution was allowed tostand at room temperature for 4 days, after which time examination ofthe ¹H and ³¹P NMR spectra of the reaction mixture revealed thatcomplete conversion to 4-PF₆ had occurred. Addition of pentane (2 mL)and diethyl ether (1 mL) afforded a pale tan precipitate, which waswashed with pentane (1 mL) and dried under vacuum. Yield of 8-PF₆: 3.2mg (31%). ¹H NMR (400 MHz, benzene-d₆) δ 3.42-3.22 (m, 3H, N—H and PNP),2.12-2.03 (m, 8H, PNP), 1.91-1.56 (m, 28H, PNP and octyl), 1.44-1.07 (m,29H, PNP and octyl), 0.76 (m, 2H, octyl). ¹³C{¹H} NMR (100 MHz,benzene-d₆): 52.1 (vt, J_(P—C)=5 Hz), 35.2 (s), 34.8 (vt, J_(P—C)=10Hz), 33.4 (vt, J_(P—C)=11 Hz), 32.6 (s), 32.3 (s), 30.4 (s), 30.2 (s),29.9 (s), 29.2 (s), 28.6, 28.5, 28.0 (vt, J_(P—C)=7 Hz), 27.9 (vt,J_(P—C)=7 Hz), 27.5 (vt, J_(P—C)=4 Hz), 27.3 (vt, J_(P—C)=5 Hz), 26.7(s), 26.6 (s), 23.5 (s), 23.1 (vt, J_(P—C)=10 Hz), 14.7 (s), −2.2 (t,J_(P—C)=21 Hz). ³¹P{¹H} NMR (162 MHz, benzene-d₆): 36.2 (s), −142.6 (h,J_(F—P)=713 Hz). IR (thin film): v_(N—H)=3241 cm⁻¹.

Synthesis of [(PNHP^(Cy))Ni(CH₃)]BPh₄. Complex 7 (24 mg, 0.045 mmol) wasdissolved in methanol (2 mL). Upon addition of NaBPh₄ (17 mg, 0.050mmol), a pale yellow precipitate formed immediately. The solid wasallowed to settle, the supernatant removed by pipette, and the solidwashed with methanol (2×2 mL). The yellow solid was dried under vacuum,and then recrystallized from hot toluene. The yellow crystals werewashed with pentane (2 mL), and dried under vacuum. Yield of[(PNHP^(Cy))Ni(CH₃)]BPh₄: 23.5 mg (62%). ¹H NMR (400 MHz, CD₂Cl₂) δ 7.35(m, 8H, BPh₄), 7.04 (t, 8H, J=7.2 Hz, BPh₄), 6.89 (t, 4H, J=7.2 Hz,BPh₄), 2.58-2.44 (m, 2H, PNP), 2.02-1.97 (m, 6H, PNP), 1.90-1.64 (m,22H, PNP), 1.52-1.23 (m, 22H, PNP), −0.58 (t, 3H, J_(P—H)=8.8 Hz,Ni—CH₃). ¹³C{¹H} NMR (100 MHz, CD₂Cl₂): 164.6 (q, J_(B—C)=49 Hz), 136.5(br s), 126.2 (q, J_(B—C)=3 Hz), 122.4 (s), 52.1 (vt, J_(P—C)=5 Hz),34.3 (vt, J_(P—C)=11 Hz), 31.2 (vt, J_(P—C)=12 Hz), 29.7 (s), 29.5 (s),29.1 (s), 28.6 (s), 27.7-27.5 (m, 2C), 27.3 (vt, J_(P—C)=6 Hz), 27.2(vt, J_(P—C)=6 Hz), 26.6 (s), 26.5 (s), 23.6 (vt, J_(P—C)=9 Hz), −21.9(t, J_(P—C)=24 Hz). ³¹P{¹H} NMR (162 MHz, CD₂Cl₂): 40.2 (s). IR (thinfilm): v_(N—H)=3183 cm⁻¹. Anal. Calcd for C₅₃H₇₆BNNiP₂: C, 74.14; H,8.92; N, 1.63. Found: C, 73.19; H, 8.76; N, 1.63.

Synthesis of (PNP^(Cy))Ni(Br). A mixture of complex 5 (105 mg, 0.159mmol) and NaOCH₃ (34 mg, 0.63 mmol) was prepared in THF (3 mL) andstirred at room temperature for 45 minutes, during which time the colorchanged from orange to dark green. Filtration through a glass woolpipette followed by solvent removal afforded a dark green residue thatwas treated with toluene (1 mL). The solvent was removed under vacuum,affording a dark green oil. Diethyl ether (1 mL) was added, and thesolvent removed under vacuum, leaving a dark green microcrystallinesolid of (PNP^(Cy))Ni(Br). Yield: 83 mg (87%). ¹H NMR (400 MHz,benzene-d₆) δ 2.71-2.59 (m, 6H, PNP), 2.12-2.07 (m, 4H, PNP), 1.92-1.54(m, 28H, PNP), 1.30-1.12 (m, 14H, PNP). ¹³C{¹H} NMR (100 MHz,benzene-d₆): 61.6 (vt, J_(P—C)=6 Hz), 33.9 (vt, J_(P—C)=11 Hz), 29.6(s), 28.7 (s), 27.8 (vt, J_(P—C)=6 Hz), 27.6 (vt, J_(P—C)=5 Hz), 27.0(s), 23.7 (vt, J_(P—C)=10 Hz). ³¹P{¹H} NMR (162 MHz, CDCl₃): 58.8 (s).Anal. Calcd for C₂₈H₅₂BrNNiP₂: C, 55.75; H, 8.69; N, 2.32. Found: C,55.88; H, 8.84; N, 2.37.

Synthesis of (PNP^(Cy))Ni(CH₃). In a small vial, (PNP^(Cy))Ni(Br) (41mg, 0.068 mmol) was suspended in diethyl ether (2 mL). Methyl lithium(50 μL of a 1.6 M solution in diethyl ether, 0.08 mmol) was addeddropwise at room temperature, the color changing from dark green tobright orange. The reaction mixture was allowed to stand for 5 minutes,and then the solvent was removed under vacuum. The orange residue wasextracted with pentane (2×2 mL), and then filtered through a glass woolpipette. The pentane was removed under vacuum, affording an orange oil.Yield of (PNP^(Cy))Ni(CH₃): 33 mg (90%). ¹H NMR (400 MHz, benzene-d₆) δ3.31-3.23 (m, 4H, PNP), 2.23-2.19 (m, 4H, PNP), 1.95-1.86 (m, 12H, PNP),1.76-1.14 (m, 32H, PNP), −0.49 (t, 3H, J_(P—H)=8.8 Hz, Ni—CH₃). ¹³C{¹H}NMR (100 MHz, benzene-d₆): 59.7 (br s), 33.7 (vt, J_(P—C)=11 Hz), 29.7(s), 28.7 (s), 28.0 (vt, J_(P—C)=6 Hz), 27.7 (vt, J_(P—C)=5 Hz), 27.2(s), 26.5 (vt, J_(P—C)=10 Hz), −25.0 (t, J_(P—C)=24 Hz). ³¹P{¹H} NMR(162 MHz, benzene-d₆): 59.2 (s).

General procedure for the hydrogenation reactions. In a WILMAD pressureNMR tube, complex 6 (ca. 5 mg, 0.006 mmol) was dissolved in THF-d₈ (0.4mL) containing hexamethylbenzene added as an internal standard. Theappropriate substrate (0.06 mmol) was added, and after recording aninitial ¹H NMR spectrum, the solvent was frozen and the headspace of thetube was evacuated. The tube was then submersed in a dewar vessel thatcontained liquid nitrogen to a level just under the TEFLON seal, and H₂(1 atm) was added. The tube was sealed while still cold, and thenallowed to warm to room temperature, which resulted in a pressure ofapproximately 4 atm (the tube headspace was measured to be 2 mL,containing ˜0.34 mmol H₂). The tube was heated at 80° C. and thereaction monitored by ¹H and ³¹P NMR spectroscopy. At the end of thereaction, the product yields were determined by ¹H NMR (integration vs.the internal standard) and verified by GC-MS (comparison of retentiontime and mass to authentic samples). Hydrogenations with complex 7 wereconducted using an analogous procedure in benzene-d₆ solvent.

In summary, transition metal complexes of nickel or cobalt were usedwith hydrogen for the catalytic hydrogenation of unsaturated compounds.The complexes included a pincer ligand that may play a role in promotingthe reaction. Although the present invention has been described withreference to various embodiments and specific details, it is notintended that such embodiments and details should be regarded aslimitations upon the scope except as and to the extent that they areincluded in the accompanying claims.

What is claimed is:
 1. A process for hydrogenation of an unsaturatedcompound, the process comprising: combining a composition comprising acompound of Formula 1 with hydrogen and an unsaturated compound underconditions effective for the hydrogenation of the unsaturated compound:

wherein: each R₁ is independently selected from cycloalkyl, alkyl,substituted alkyl, phenyl, or substituted phenyl; R₂ is —CH₂Si(CH₃)₃, H,alkyl, substituted alkyl, phenyl, substituted phenyl, alkoxide, oramido; and M is cobalt or nickel.
 2. The process of claim 1, wherein R₂is —CH₂Si(CH₃)₃, H, or alkyl.
 3. The process of claim 1, wherein R₂ is—CH₂Si(CH₃)₃, H, CH₃, or CH₂(CH₂)₆CH₃.
 4. The process of claim 1,wherein the unsaturated compound comprises: a carbon-carbon double ortriple bond that becomes hydrogenated as a result of the process, acarbon-oxygen double bond that becomes hydrogenated as a result of theprocess, or a carbon-nitrogen double or triple bond that becomeshydrogenated as a result of the process.
 5. The process of claim 1,wherein the combining the composition with hydrogen further comprisesadding Hg or water.
 6. The process of claim 1, wherein the combining thecomposition of Formula 1 with hydrogen comprises combining a solution ofthe composition with the hydrogen and the unsaturated compound.
 7. Aprocess for hydrogenation of an unsaturated compound, the processcomprising: combining a composition comprising a compound of Formula 1or Formula 2 with hydrogen and an unsaturated compound under conditionseffective for the hydrogenation of the unsaturated compound:

wherein: each R₁ is independently selected from cyclohexyl, isopropyl,adamantyl, or phenyl; R₂ is —CH₂Si(CH₃)₃, H, alkyl, substituted alkyl,phenyl, substituted phenyl, alkoxide, or amido; M is cobalt or nickel;and X is a counterion.
 8. The process of claim 7, wherein R₂ is—CH₂Si(CH₃)₃, H, or alkyl.
 9. The process of claim 7, wherein R₂ is—CH₂Si(CH₃)₃, H, CH₃, or CH₂(CH₂)₆CH₃.
 10. The process of claim 7,wherein the unsaturated compound comprises: a carbon-carbon double ortriple bond that becomes hydrogenated as a result of the process, acarbon-oxygen double bond that becomes hydrogenated as a result of theprocess, or a carbon-nitrogen double or triple bond that becomeshydrogenated as a result of the process.
 11. The process of claim 7,wherein the combining the composition of Formula 1 or Formula 2 withhydrogen further comprises adding Hg or water.
 12. The process of claim7, wherein the combining the composition of Formula 1 or Formula 2 withhydrogen comprises combining a solution of the composition of Formula 1or Formula 2 with the hydrogen and the unsaturated compound.
 13. Theprocess of claim 7, wherein the compound comprises:(PNP^(Cy))Co(CH₂SiMe₃), [(PNHP^(Cy))Co(CH₂SiMe₃)][X], (PNP^(Cy))Co(H),[(PNHP^(Cy))Co(H)][X], (PNP^(Ad))Co(CH₂SiMe₃),[(PNHP^(Ad))Co(CH₂SiMe₃)][X], (PNP^(iPr))Co(CH₂SiMe₃),[(PNHP^(iPr))Co(CH₂SiMe₃)][X], (PNP^(Cy))Ni(H), [(PNHP^(Cy))Ni(H)][X],(PNP^(Cy))Ni(CH₂(CH₂)₆CH₃), [(PNHP^(Cy))Ni(CH₂(CH₂)₆CH₃)][X],(PNP^(Cy))Ni(CH₃), or [(PNHP^(Cy))Ni(CH₃)][X], wherein: Cy iscyclohexyl, Ad is adamantyl, iPr is isopropyl, and X istetraphenylborate, hexafluorophosphate, B(C₆F₅)₄, or B(3,5-(CF₃)₂C₆H₃)₄.14. The process of claim 13, wherein X is tetraphenylborate orhexafluorophosphate.
 15. A composition comprising a compound representedby Formula 1 or Formula 2:

wherein: each R₁ is independently selected from cyclohexyl, isopropyl,adamantyl, or phenyl; R₂ is —CH₂Si(CH₃)₃, H, alkyl, substituted alkyl,phenyl, substituted phenyl, alkoxide, or amido; M is cobalt or nickel;and X is a counterion.
 16. The composition of claim 15, wherein R₂ is—CH₂Si(CH₃)₃, H, or alkyl.
 17. The composition of claim 15, wherein R₂is —CH₂Si(CH₃)₃, H, CH₃, or CH₂(CH₂)₆CH₃.
 18. The composition of claim15, wherein the compound is represented by Formula 2 in which thecounterion X is tetraphenylborate, hexafluorophosphate, B(C₆F₅)₄, orB(3,5-(CF₃)₂C₆H₃)₄.
 19. The composition of claim 15, wherein thecompound comprises: (PNP^(Cy))Co(CH₂SiMe₃),[(PNHP^(Cy))Co(CH₂SiMe₃)][X], (PNP^(Cy))Co(H), [(PNHP^(Cy)Y)Co(H)][X],(PNP^(Ad))Co(CH₂SiMe₃), [(PNHP^(Ad))Co(CH₂SiMe₃)][X],(PNP^(iPr))Co(CH₂SiMe₃), [(PNHP^(iPr))Co(CH₂SiMe₃)][X], (PNP^(Cy))Ni(H),[(PNHP^(Cy))Ni(H)][X], (PNP^(Cy))Ni(CH₂(CH₂)₆CH₃),[(PNHP^(Cy))Ni(CH₂(CH₂)₆CH₃)][X], (PNP^(Cy))Ni(CH₃), or[(PNHP^(Cy))Ni(CH₃)][X], wherein: Cy is cyclohexyl, Ad is adamantyl, iPris isopropyl, and X is tetraphenylborate, hexafluorophosphate, B(C₆F₅)₄,or B(3,5-(CF₃)₂C₆H₃)₄.
 20. The composition of claim 19, wherein X istetraphenylborate or hexafluorophosphate.